Dental System for Trans-illumination of Teeth

ABSTRACT

In a dental system for the transillumination of teeth having a light source for producing examination radiation, irradiation means for directing the examination radiation at a tooth to be examined, and means for acquiring an optical image of the tooth illuminated by the examination radiation, the irradiation means includes light-guiding and/or light-deflecting elements, at least the light-guiding and/or light-deflecting element facing the tooth to be examined being embedded in a transparent, flexible coupling body that is provided to rest on the tooth or the gingiva of the tooth.

The present invention relates to a dental system for the transillumination of teeth according to the precharacterizing clause of claim 1, which system has a light source for producing examination radiation, irradiation means for directing the examination radiation at a tooth to be examined, and means for acquiring an optical image of the tooth illuminated by the examination radiation.

In medicine, in particular in dentistry, diagnostic systems based on optical principles are increasingly being used. The reason for this is that such devices usually allow a diagnosis to be made without contact, that is to say in particular in a pain-free manner, and, in addition, often also provide optical images with which any necessary therapeutic measures can be communicated to the patient graphically and hence more clearly. For example, so-called intraoral cameras are used in dentistry, which cameras include a handpiece, the front end region of which is introduced into the mouth of a patient. In that end region there is generally a light-entry or viewing window for the camera lens, from which the image of the object to be examined is transmitted to an acquisition device, for example a CCD chip.

Such an intraoral camera can further be extended to a system for the transillumination of teeth, as is known inter alia from DE 10 2006 041 020 A1 of the applicant. In that system, the tooth to be examined is irradiated with light within a specific wavelength range, an optical image of the tooth illuminated by the examination radiation then being acquired and evaluated. Because carious areas in the tooth scatter the light differently than healthy dental tissue, such areas can be identified when the tooth is observed with the aid of a camera, it even being possible, if the system is suitably configured, to obtain a more reliable caries diagnosis than is the case with a conventional X-ray examination.

The quality of the images produced in this procedure, and hence ultimately of the caries diagnosis, is dependent to a critical extent on the way in which the light is coupled into the tooth to be illuminated. In DE 10 2006 041 020 A1 there is used for that purpose a special head-piece of an instrument, which rests on the tooth. If excessive irradiation occurs as a result of illumination of the light sensor directly or by reflection, a computational elimination of those image regions is carried out. However, this has the disadvantage that the dynamic range of the system is limited on account of the computational possibilities.

As an alternative thereto there is known from U.S. Pat. No. 4,184,175 a polarizing filter for removing reflected light or direct light. However, the polarization causes a loss in intensity in the illumination of the tooth, which represents a not inconsiderable disadvantage. Finally, U.S. Pat. No. 6,672,868 describes a device which has mechanical means for blocking light, by which the direct ingress of reflected light or direct light in the light sensor is reduced. However, such measures result in an enlarged construction of the front end region of the device, which is a disadvantage because of the already restricted room for maneuver inside the oral cavity of the patient.

Accordingly, the object underlying the present invention is to provide a novel solution for the production of a system for the transillumination of teeth, in which the above-mentioned disadvantages are avoided. In particular, effective and reliable coupling of the light into the tooth that is to be transilluminated is to be ensured.

The object is achieved by a dental system for the transillumination of teeth having the features of claim 1. Advantageous further developments of the invention are the subject of the dependent claims.

The solution according to the invention is based on the idea of optimizing the manner in which light is coupled into the tooth that is to be transilluminated. To that end, it is proposed according to a first aspect of the present invention to embed a light-guiding or light-deflecting element, which faces the tooth to be examined and with the aid of which the light is ultimately directed at the tooth, in a transparent, flexible coupling body which is provided to rest on the tooth or the gum, the so-called gingiva.

According to this first aspect of the present invention there is accordingly proposed a dental system for the transillumination of teeth which has a light source for producing examination radiation, irradiation means for directing the examination radiation at a tooth to be examined, and means for acquiring an optical image of the tooth illuminated by the examination radiation, wherein the irradiation means include light-deflecting and/or light-guiding elements and wherein at least the light-guiding and/or light-deflecting element facing the tooth to be examined is embedded in a transparent, flexible coupling body which is provided to rest on the tooth or on the gingiva of the tooth.

Because the coupling of light into the tooth is carried out with the aid of the flexible coupling body, the emergence of interfering light from the light-guiding element is prevented or at least reduced. A maximum degree of coupling of the light into the tooth substance or gingiva is obtained, which ultimately leads to improved images of the tooth to be examined.

The coupling geometry of the transparent coupling body can consist of a plane face, a sphere, a spherical segment, a concave or convex face or a free-form face. Those faces can then advantageously be equipped with an additional structure which prevents light that cannot be coupled into the hard tooth tissue and/or gingiva from being reflected at the tooth and/or gingiva and leading to overexposure of the image recording sensor or other light-sensitive detector. The mode of operation of this principle is based on the fact that light beams are partially deflected at the faces of the additional structure as long as the corresponding structures do not come into contact with the hard tooth tissue and/or gingiva. The effect is based on the difference in refractive index between the contact material and air, which allows light to exit the coupling body only at specific angles. If the structures of the coupling body are not resting on the tooth or gingiva, more light is reflected back, due to the conditions, and not decoupled. Geometries in the form of pyramids, cones, waves and waves with any desired suitable structure which is distributed periodically and/or non-periodically are suitable for these additional structures.

As well as improving the coupling of light into the tooth to be examined, a further function of the coupling body is to protect the light-guiding and/or light-deflecting elements, by means of which the light from the light source is directed at the tooth, from external influences. This is important because it is absolutely necessary for hygiene reasons regularly to clean, but in particular also to sterilize, the area of the device that is introduced into the oral cavity of the patient. By embedding the light-guiding/light-deflecting elements, they are better protected so that they are not damaged by the sterilizing operation, in which the device is exposed to high temperatures as well as to high humidity. It is possible in particular for light guides which extend from a light source to the light decoupling point to be embedded in the transparent material of the coupling body. At the frontmost end of the light guide there can be located a prism, which ultimately effects deflection of the beam in order to direct the light at the tooth to be examined. It has been shown that the protective action for the elements for light transmission can additionally be improved if a hydrophobic coating is used. This could be applied, for example, directly to the light guide or to a sheathing of the light guide, in order to prevent moisture from penetrating into the underlying components and damaging them. For example, the material Parylene could be used for this purpose.

A further advantageous measure of the present invention serves to avoid, or at least reduce, the formation of so-called speckle, which is caused by interference phenomena in human tissue. To that end, it is proposed to irradiate the tooth to be examined with a comparatively small spectral bandwidth in the range from 2 to 10 nm.

It is further possible according to the invention for a particular arrangement of the light sources inside the hand-held device to be provided. This particular arrangement is attributable to the fact that light guides are used for the transmission of the light but, owing to the space required for image transmission to the image acquisition means, they are not able to run centrally through the hand-held device. In that case, an inclined orientation of the light sources relative to the longitudinal axis of the handpiece has been found to be advantageous because, in that manner, maximum transmission of the emitted light can be achieved while, at the same time, the bending radius of the light guide can be optimized and—as will be explained in detail hereinbelow—as small a construction as possible for the handpiece is possible.

Finally, according to a further aspect of the present invention there is proposed a specially designed attachment for passing light through a tooth to be examined, in which the tooth is illuminated from one side and the image of the illuminated tooth is acquired from the opposite side. Because the attachment is mounted to be removable from the handpiece but is fixed relative to the longitudinal axis of the handpiece, the operation is made much easier and a substantial saving in terms of working time is achieved, because the viewing direction can be changed immediately.

Ultimately, because of the measures described above, on the one hand the quality of the images that can be obtained, and hence the reliability of the caries diagnosis, is improved and on the other hand handling of the device is simplified.

The invention is to be explained in greater detail hereinbelow with reference to the accompanying drawing, in which:

FIG. 1 shows a view of a first embodiment of a hand-held device for the transillumination of teeth;

FIG. 2 shows an enlarged view of the front end region of the hand-held device;

FIG. 2 a shows schematically the coupling of the light into the gingiva;

FIG. 3 shows a sectional view of the device of FIG. 1;

FIG. 4 shows a view of the arrangement of the light sources inside the hand-held device;

FIGS. 5-8 show different views of the front end region of the attachment of the hand-held device with the passage of the light guides used for light coupling;

FIGS. 9-12 show views of the light guide holder with the transparent coupling body;

FIG. 13 shows the transparent coupling body with the deflecting prism located therein;

FIGS. 14 and 15 show views of the light guide with the deflecting prism located on it at the front end;

FIG. 16 shows schematically the delivery of the light via the coupling body;

FIGS. 17 to 19 show different views of a structure located on the surface of the coupling body;

FIG. 20 shows the mode of operation of the structure provided on the coupling body;

FIG. 21 shows a perspective view of an alternative attachment for light coupling and image acquisition of the device according to the invention;

FIG. 22 shows a sectional view of the attachment of FIG. 20; and

FIGS. 23 to 25 show systematic views relating to the use of the attachment of FIG. 21.

The transillumination method on which the present invention is based will first be explained in principle.

The transillumination method is based on passing visible light through a tooth, that is to say transilluminating it. To that end, examination radiation is generated with the aid of a light source and is directed at the tooth. The examination radiation is usually in a wavelength range of approximately from 550 μm to 790 μm, for example approximately 670 μm. The tissue of the tooth does not completely block the examination radiation but instead allows the light to pass through the tooth. The radiation is thereby partially scattered, carious regions in particular having a characteristic effect on the light. If the tooth transilluminated in that manner is viewed from different viewing directions, such carious regions can be detected because they appear slightly darker. In particular when images taken at different times are compared with one another, caries can thus be detected comparatively effectively and also in good time.

A device using this principle is shown in FIG. 1 and is denoted generally by the reference numeral 1. It comprises as a fundamental component an elongate hand-held device 2 having a handle 3 in which the fundamental components for illuminating the tooth to be examined and for image acquisition are arranged. There are located inside the handle 3 in particular light sources for producing examination radiation, as well as image acquisition means, for example in the form of a CCD chip for recording an image of a tooth illuminated with the aid of the light. The data provided by the image acquisition means are then transmitted to a central processing unit. To that end, a cable 4, at the end of which there is a USB connector 5, extends from the rear end of the handle 3, via which cable 4 a connection to a PC can be made in a simple manner. The image information can then be stored and analyzed in the PC (not shown). Instead of the USB connector shown, the hand-held device 2 could also be connected to a central processing unit by other means. However, the USB connection has been found to be particularly advantageous because the device 1 can thereby at the same time also be supplied with power.

The arrangement of the light sources and of the image acquisition means inside the handle 3 of the handpiece 2 firstly has the advantage that those components are here comparatively well protected from external influences. The actual illumination of the tooth is carried out with the aid of an attachment 10 which is detachably arranged at the front end of the handle 3. As is shown in the sectional view of FIG. 3, the handle 3 has at its front end a cylindrical pin 6 on which the attachment 10 is fitted. At the front end of the attachment 10 there are formed two lateral arms 11, via each of which, according to the representation of FIG. 2, the light can be directed at lateral surfaces of a tooth 100 to be examined or at the gum of the tooth 100, the so-called gingiva. As is shown in FIG. 2 a, the light coupling is here ideally effected slightly obliquely in the upper end region of the gingiva, because it has been shown that the highest contrast for the transilluminated tooth 100 is achieved in that case. The more detailed configuration of the arms 11 with the elements for light transmission located therein will be explained in detail hereinbelow.

The light entry for observation of the illuminated tooth is carried out with the aid of a window formed on the underside of the front end region 12 of the attachment 10. The cylindrical pin 6 of the hand-held device 2 extends into the front end region 12 of the attachment 10 so that light is able to enter a deflecting prism 7 via the window. Incoming light beams are deflected by the deflecting prism 7 in such a manner that they are directed at the image acquisition means, that is to say, for example, the CCD chip 8, located in the handle 3. The deflecting prism 7 is so configured that a deflection of the beams by an angle of approximately 90°, preferably of slightly less than 90°, is achieved.

As is clear from FIG. 3, the image of the illuminated tooth 100 is accordingly reflected centrally through the hollow-cylindrical projection 6 to the CCD chip 8. This means that light guides for transmitting the light that extend along the handpiece 2 should, if possible, extend at the edge in order not to impair the transmission of the image. In order to achieve optimum light transmission, a special arrangement and orientation of the light sources and light guides is proposed, which is to be explained hereinbelow with reference to FIGS. 3 and 4.

The problem is that, for reasons of space, although the light sources, which are provided with the reference numeral 9 in the drawings, are to be arranged approximately centrally inside the handle 3, the light guides themselves are to extend at the edge. At the same time, however, the light guides are to be bent to only a specific radius in order to ensure optimum light transmission. To that end it is proposed to arrange the light sources 9 at an angle of approximately 50 to 60° relative to the longitudinal axis of the handpiece. This inclined position of the light sources 9 can be seen in particular in the view in FIG. 4, which shows the inclined placement of the light sources 9 on the plate for the camera electronics. This inclined position has the result that the bending radius of the light guide 9 a extending immediately from the light sources to the front side of the handpiece 2 can be kept within a range in which maximum light transmission is ensured. At the same time, the dimensions of the handle 3 can be minimized so that a handpiece 2 that is comparatively compact and hence easy to handle is achieved. As an alternative to the embodiment shown, it is also possible for the light sources to be integrated into the housing of the handpiece 2. In that case, they are connected to the camera plate via an electric cable.

The light guides 9 a, one of which is shown in each of FIGS. 3 and 4, extend to a front shoulder 6 a on the underside of the projection 6. When the attachment 10 is in the fitted state, the front ends of the light guides 9 a are aligned with end faces of further light guides 9 b, which extend inside the attachment 10 to its front end into the end regions of the two arms 11. This configuration and arrangement of these continuing light guides 9 b is to be explained in greater detail hereinbelow with reference to FIGS. 5 to 15.

Firstly, FIGS. 5 to 8 show different views of the front end region of the attachment 10, the view of the outer sheathing of the attachment 10 having been omitted in FIGS. 6 and 7 so that the passage of the light guides can be seen. FIGS. 14 and 15 in turn show individual light guides 9 b, which consist, for example, of plastics material, glass fiber bundles optionally with partially cemented fibers, single glass fibers, a fiber rod or similar materials and accordingly have a certain flexibility. The light guides 9 b are connected at their fronts end with a deflecting prism 15 via which—as will be explained in greater detail hereinbelow—the light is deflected approximately perpendicularly and accordingly directed at the tooth to be examined. Coupling of the light guide 9 b to the deflecting prism 15 can be carried out by injection-molding or the like.

An optical material whose refractive index is lower than the refractive index of the plastics light guide is preferably injection-molded around the flexible light guides 9 b. As a result of this material, which can be, for example, self-adhesive silicone, the total reflection required for optimum light transmission is made possible.

For beam deflection, the deflecting prism 15 already mentioned is injection-molded at the exit end of the light guide 9 b, it being possible for the deflecting prism 15 additionally to be provided with a coating on the reflection face 15 a for the purpose of better transmission. The light exit side 15 b could, in turn, additionally be provided with an optical lens structure, whereby it is possible to influence the light beam.

A particular feature is that the two—optionally sheathed—light guides 9 b with the prisms 15 located thereon are embedded in a corresponding element which is referred to hereinbelow as the light guide holder 20 and is shown in greater detail in FIGS. 9 to 12. The light guide holder 20 firstly has a base portion 21 from the end region of which the ends of the light guides 9 b extend. The light guides 9 b initially run in parallel in the base portion 21, but they then branch into two arms 22 of the light guide holder 20, which extend towards the front end. At the front end, the arms 22 have head regions 23 in each of which the deflecting prisms 15 are arranged. To that end, two laterally projecting pins 16 are provided on the deflecting prisms, via which the prisms 15 are anchored in the end regions 23 of the light guide holder 20. At least the front end regions 23 of the light guide holder 20 are made of a transparent or light-permeable material, although the production of the light guide holder 20 as a whole is simplified if the entire element is made of the same transparent and flexible material.

The result of the embedding of the light guides 9 b in the light guide holder 20 is that the light guides 9 b are better protected from external influences. This is important because the light guide holder 20 is arranged on the attachment 10, which for hygiene reasons must be regularly cleaned, in particular also sterilized. Because the light guides 9 b and the deflecting prism 15 are completely surrounded by the light guide holder 20, those optical elements for light transmission are better protected from external influences. An additional improvement in the protection can be achieved by preventing, or at least greatly reducing, the ingress of water into the light guide 9 b by means of a suitable hydrophobic coating. The background to this improvement is that the light guide 9 b, which is preferably sheathed in silicone, is exposed to a vapor overpressure atmosphere during autoclaving. By means of diffusion processes, the water passes through the outer layers of material into the plastics light guide 9 b, which can lead to premature ageing or to damage in the form of the release of frozen-in stresses. By applying a hydrophobic layer, for which the material Parylene, for example, can be used, moisture is prevented from penetrating into the underlying components and damaging them. The hydrophobic layer can be applied either directly to the plastics light guide or to the outermost silicone layer of the plastics light guide sheathed in silicone.

A further advantage of the embedding of the light guides 9 b and of the deflecting prisms 15 in the light guide holder 20 is that the coupling of light into the tooth to be examined can be optimized. As is shown by FIG. 16 and in particular also FIG. 13, which shows a sectional view of the front end region 23 of the light guide holder 20 with the deflecting prism 15 embedded therein, the light is ultimately irradiated into the tooth via the transparent end region 23, which is also referred to hereinbelow as the coupling body.

Because the coupling body 23 is made of a flexible transparent material, it can rest as flat as possible on the outside of the tooth or gingiva. This contact has the result that the formation of reflections or stray radiation, which could enter the entry window of the attachment 10 directly, is suppressed. Interfering reflections in the image of the illuminated tooth can thus be reduced. Flat application of the light coupling body 23 is preferably assisted by the fact that the arms 11 of the attachment 10 are also made of a flexible material and have a certain bias, as a result of which the arms 11 mould to the lateral walls of the tooth when in the fitted position thereon.

The coupling of light into the tooth can further additionally be optimized by a special form of the surface of the coupling body 23, which is initially approximately spherical. Conceivable surface structures therefore are shown in FIGS. 17 to 19. Geometries in the form of pyramids, cones, waves and waves with a corresponding structure which is distributed periodically and/or non-periodically can be used. The purpose of this structure is to improve further the coupling of the light into the hard tooth tissue and/or the gingiva and at the same time prevent light that cannot be coupled from being reflected at the hard tooth tissue and/or gingiva, which would lead to undesirable overexposure of the image-recording sensor. The mode of operation of this structure is based on the fact that light beams are partially deflected at the faces of the structures as long as the structures do not come into contact with the hard tooth tissue and/or the gingiva. This effect is based on the difference in refractive index between the contact material and air. This difference gives a corresponding angle of total reflection, light beams that are incident on the surface of the structure at a smaller angle being reflected back, as is shown schematically in FIG. 20. However, if the structure comes into contact with the hard tooth tissue and/or the gingiva, the geometrically determined light exit faces are deformed, which leads to a change in the angle at which the light beam is incident on the boundary surface. This in turn allows the light beams to leave the light coupling body 23 and pass into the hard tooth tissue.

A further possibility for avoiding overexposure would consist in the use of polarizing filters on both the light-exit side and the light-entry side and/or in the optical system of the detection device. The filters are so oriented that direct irradiation of the light-exit end on the light-entry side is prevented.

Finally, an advantage of the embedding of the light guides 9 b with the deflecting prisms 16 in the light guide holder 20 is also that the light guide holder 20 can be replaced in a simple manner should this be necessary as a result of ageing phenomena. It is not necessary in this case to replace the entire attachment 10, for which reason the outlay in terms of cost for corresponding maintenance work can be reduced.

The measures described hereinbefore contribute in particular to achieving improved coupling of light into the tooth to be examined. A further improvement in the system can further also consist in using light having a comparatively small spectral bandwidth in the range from 2 to 10 nm. This has the advantage in particular that so-called speckle, which is caused by interference phenomena in human tissue, can be avoided or at least markedly reduced. This also contributes towards optimizing the results of the examination.

Finally, FIGS. 21 to 25 show a further attachment 110 which could be used in the device according to the invention for caries diagnosis. In contrast to the attachment 10 discussed hereinbefore, this further attachment 110 has only a single arm 111, through which there extends a light guide 109 having a deflection element 115 at the front end. The end region 112 having a light-entry window 113 is in turn arranged opposite the front end of the arm 111. When the attachment 110 is fitted to the handle 3 of the handpiece 2, the deflecting prism 116 is located directly behind the entry window 113, with the aid of which deflecting prism the light incident on the tooth 100 to be examined is directed to the image acquisition means.

The mutually opposing arrangement of the deflection element 115 and the light-entry window 113 has the result that, with the aid of the attachment 110, the tooth 100 to be examined can either be illuminated from the so-called buccal tooth surface and observed from the lingual tooth surface or alternatively illuminated from the lingual tooth surface and observed from the buccal tooth surface. Compared to embodiments conventional hitherto, such a changeover does not require the attachment to be replaced, which makes the operation much easier and represents a considerable time saving. Furthermore, it is also not necessary to remove the handpiece from the workspace, that is to say the oral cavity of the patient, and two-handed operation is not required in order to change the viewing direction. The attachment 110 is so arranged on the handpiece 2 that it cannot be twisted. Ergonomic handling is thereby achieved.

In this embodiment of the attachment 110 too, the light guide 109 having the deflection element 115 can be embedded in a transparent flexible element. That is to say, the above-described measures for improving the coupling of light into the tooth can also be used here.

Overall, therefore, a dental system for the transillumination of teeth is produced which allows images of very high quality to be produced, which ultimately leads to a marked improvement in the detection of caries. 

1. Dental system for the transillumination of teeth, having comprising: a light source for producing examination radiation, irradiation means for directing the examination radiation at a tooth to be examined, and means for acquiring an optical image of the tooth illuminated by the examination radiation, wherein the irradiation means includes light-guiding and/or light-deflecting elements, wherein at least the light-guiding and/or light-deflecting element facing the tooth to be examined is embedded in a transparent, flexible coupling body that is provided to rest on the tooth or on the gingiva of the tooth.
 2. Dental system according to claim 1, wherein the coupling body, in a region provided for light coupling, has the geometry of a face, a sphere, or a spherical segment, or is convex or concave.
 3. Dental system according to claim 2, wherein the coupling body is provided with an additional structure in its region provided for light coupling.
 4. Dental system according to claim 1, wherein the irradiation means includes at least one light guide embedded in the material of the coupling body.
 5. Dental system according to claim 4, wherein the coupling body is part of a light guide holder in which the light guide is embedded.
 6. Dental system according to claim 4, wherein a deflecting prism is arranged at an end of the light guide on a light-exit side, which deflecting prism is embedded in the coupling body.
 7. Dental system according to claim 4, wherein the light guide and/or a sheathing of the light guide has a hydrophobic coating.
 8. Dental system according to claim 1, wherein the light source is configured to emit light having a spectral bandwidth in the range from 2 nm to 10 nm.
 9. Dental system according to claim 1, comprising a handpiece in which the light source is arranged, the light source being inclined relative to a longitudinal axis of the handpiece.
 10. Dental system according to claim 1, comprising a handpiece and at least part of the irradiation means is arranged in a removable attachment, wherein the attachment cannot be twisted relative to the longitudinal axis of the handpiece. 